Rank some elements by ascending date

rank-by-date.py

# coding: utf-8

"""rank by ascending date
"""

from datetime import date

from faker import Factory

import pandas as pd
import numpy as np


FAKE = Factory().create()


def fake_id(number):
    f = lambda : FAKE.lexify('???').lower() + FAKE.numerify('#')
    possible = [f() for _ in range(number // 10)]
    return np.random.choice(possible, size=number).tolist()

def fake_date(number):
    f = lambda: FAKE.date_time_this_decade().date()
    return [f() for _ in range(number)]

def count_demande(df, idx, date):
    return len(df[(df.idx == idx) & (df.date < date)])


if __name__ == '__main__':
    nrows = 100
    df = pd.DataFrame({"idx": fake_id(nrows),
                       "date": fake_date(nrows)})
    df = df.reindex_axis(['idx', 'date'], axis=1)
    df['date'] = df['date'].apply(pd.Timestamp)
    df['nb_demande'] = df.apply(lambda row: count_demande(df, row.idx, row.date), axis=1)
    # or
    df['nb_demande_bis'] = df.groupby('idx')['date'].rank()